Continuous inductive train control system



Oct. 4, 1938. w. H. HOPPE CONTINUOUS INDUCTIVE TRAIN CONTROL SYSTEM Filed Jan. 15, 1957 2 Sheets-Sheet 1 a. r ATTORNEY N Om ZOU Oct. 4, 1938. w. H. HOPPE CONTINUOUS INDUCTIVE TRAIN CONTROL SYSTEM Filed Jan. 15, 1957 2 Sheets-Sheet 2 TO 7 a ATTORNEY N, .E V m Patented Oct. 4, 1938 CONTINUOUS INDUCTI SYST vn TRAIN CONTROL 1 WalterH. Hoppe, Rochester, N. Y.,-assignor to General Railway Signal Company, .ltochester,

Application January13, 1937, Serial No.'120,421

14 Claims. (01. 246- 63) This invention relates to automatic train control systems for railroads and it more particularly pertains to systems commonly known as the continuous inductive track circuit type.

The present invention is in the nature of an improvement in the invention disclosed in Bushnell-Reichard application, Ser. No. 112,858, filed November 2'7, 1936.

Generally speaking and without attempting to define the nature or scope of the invention, it is proposed to provide a three indication, continuous inductive system dependent upon current in both track rails, the track circuit being automatically and continuously checked for occupancy, broken rails, cross connectionsand the presence of rail current in each rail.

More specifically, the present invention makes use of phase and magnitude controlled gaseous arc discharge vacuum tubes, which are selectively responsive to different frequencies and combinations of frequencies of alternating current applied to the track rails in accordance with traffic conditions, for producing the variousindications on a moving vehicle.

One type of phase and magnitude controlled gaseous arc discharge tube employed in the present invention is of such construction that when the anode or plate swings positive and a certain potential is applied to the grid or control electrode, the tube will fire and current will flow from the anode to the cathode or filament. As soon as the plate current begins to flow the grid is instantly surrounded by a sheath of positive ions and the grid has no further effect in controlling the plate current. This sheath, usually only a fraction of a millimeter thick, contains the whole voltage drop due to the grid voltage, increasing the grid voltage merely changes the thickness of the sheath and has no effect on the potential of the rest of the space unless the plate current flowing is of very small magnitude and/ or unless the grid control energy can be tremen dously increased. Practical application, however, excludes the last two possibilities. Therefore the grid loses control over the plate current, when once it is started and plate current flow can only be stopped by removing the plate voltage.

The function of the grid may therefore be likened to a trigger, the amount of power required-to start the tube being exceedingly small and when the tube is once fired it continues to conduct until plate energy is removed. From the above discussion it will be apparent that an alternating current voltage applied to the plate circuit of such a. tube can only be controlled during-positive swings of this, voltage for efiecting plate current flow, with thenegative swings being ineffective because the proper polarity is not appliedjto the plate. A thermionic tube having thecharacteristics above discussed is disclosed in Langmuir Patent No. 1,289,823. The name Thyratron has been applied to tubes .of this type and in thefollowing description TR and TB, of Fig.1 will be referred to as Thyratron'tub es.""

Regarding the phase andmag'nitud e control of the 'Thyratroni tube, when an alternating voltage is applied to the plate circuit, the grid has an opportunity of regaining control once each cycleand can delay the starting of the are for as long a period during the subsequent positive half cycle asthe'grid'voltage is sufiiciently negative." This means that the grid can controlthe average current flowing through the tube and this averaging can be made as fine grained as desired by increasing the frequency of interruption. From thev above it will be apparent thatcurrent flow in the plate circuit of'the"Thyratron tube depends upon the proper phase relation between the plate circuit voltage and the grid circuit voltage, as well as upon the proper polarity and magnitude of these voltages.

From the above .discussion and as later pointed out indetail, it'will be observed'that absence of current in the track rails, denoting occupancy or broken rails, as 'well as abnormal circuit conditions due to the" presence of current in each rail flowing in the same instantaneous direction, are ineffective toeffect the control of the relays in the output circuitsof the illustrated Thyratron tubes.

One object of the present invention is the provision of a three indication, continuous inductive system of control, whereby trackway conditions willdeterminethe presence of current of one fre quency, current of another frequency and the absence of current in the track rails.

Another object of the presentinvention is the transmission of these ,frequencies to a moving vehicle in a simple and direct manner and the positive selective operationof indicating devices on the vehicle in response to the reception and non-reception oi alternatingcurrent of the two Fig. 2 illustrates that the two sources of alter- V nating current f and I have a single common return COM.

Fig. 3 indicates the arrangement of the intermediate tap battery used in 4, having end. terminals (3+) and (B) and intermediate terminal (CN).

Fig.4 illustrates in diagrammatic form a modified form of trackway apparatus and associated car carried equipment, together with the circuit organization in accordance with the present invention. I

Apparatus Referring to Fig. 1, the trackway'apparatus has been illustrated as applied to a railway track having rails l divided by insulating joints 2 into sections A. B, C and D."

Each section is provided with a track circuit comprising the track rails themselves, a circuit including a supply transformer T1 (with suitable exponent) connected in series'with a track battery B and limiting resistance R (with suitable exponent) at the exit end of the section for supplying direct current and superimposed alternating current to the rails. 'These band pass filters BPF and BPF allow a band of frequencies embracing both frequencies f and f to flow. The track circuit includes a track relay T (with suitable exponent) at the entrance end of each section.

Although wayside signals are ordinarily located at the entrance to each section and controlled in accordance with trafiic conditions, for the sake of simplicity these signals S, S and S are merely indicated, with their control circuits omitted, since their control forms no part of the present invention.'

A first source of alternating current (for example, cycles) and a second source of alter nating current (for example, cycles) are provided at the entrance of each. section and selectively applied to the exit end of the next section to the rear by means of the transformer in ac cordance with the position of the track relay. For example, frequency f (140 cycles) is applied to the exit end of the next section to the rear when the track relay is picked up and frequency f (90 cycles) is applied to the same section when the track relay is dropped away.

Mounted in advance of the Wheels and axles W of the vehicle are receiving coils RC and RC so located that the current flow at any instant through one rail in' one direction and back through the other rail in the other direction induces currents in these receiving coils 'of the same frequency as that flowing in the track rails. Under these normal conditions the separate voltages induced in receivers RG and RC are fed to voltage amplifiers, the voltage of receiver RC being applied to the input circuits of the voltage amplifier comprising vacuum tubes IVA and 2VA by way of band pass filter BPF and transformer I TF The voltage induced in the winding of receiver RC is applied to the input circuits of the voltage amplifier comprising vacuum tubes IVA and 2VA by way of bandpass filter BPF and transformer ITF These band pass filters .BPF and BPF allow a band of frequencies embracing both frequencies f and f to flow. Transformers ITF' and ITF have their pri-' maries connected to the output of the associated band pass filters and each transformer has two secondary windings, one tuned to frequency f and the other tuned to frequency 1 so that frequency f appears in the output circuit of tubes IVA and 2VA While frequency f appears in the output circuits of tubes IVA and 2VA The secondary windings of transformers ITF and ITF have such leakage reactance values that condensers IC 2C IC and IC connected across these'windings render them selectively responsive only to the frequencies as above discussed. It will be understood that tubes IVA ZVA IVA and ZVA are of. the ordinary voltage amplifier type.

The output circuits of tubes IVA and IVA which amplify currents of frequency f and frequency f respectively, when currents of these frequencies flow in the track rails, are connected to the input-circuits of power amplifier tubes PA and PA respectively, by means of secondary windings of transformers ZTF and 2'I'F connected in the output circuits of the voltage amplifier tubes. These secondary windings are tuned to frequencies f and f by condensers 3C and 30 respectively. It will be understood that tubes PA and PA are of the ordinary power amplifier type.

Frequency f appearing in the plate circuit of power amplifier PA? is applied to the plate circuit of Thyratron TR by means of transformer iTF and in this plate circuit is connected relay F tuned to be responsive to frequency f by means of condenser 40 Frequency 1 appearing in the output of power. amplifier PA is applied to the plate circuit of Thyratron 'I'RF, being connected in the Thyratron plate circuit and tuned to frequency f by condenser 4C The input or grid circuit of Thyratron TR receives a negative grid bias .voltage from current of frequency f by means of the lower secondary winding of transformer 2TF in series with rectifier unit RT. The grid or input circuit of Thyratron TR, has induced therein a negative grid bias voltage derived from frequency f applied thereto by means of the lower secondary winding of transformer 2TF with rectifier unit RT connected in this circuit. These rectifiers and circuit connections to the input circuits of the Thyratron tubes are for the purpose of applying the proper negative bias to the grids of these tubes when'these Thyratron tubes are called upon to function.

A phase shifter connected to the secondary winding of transformer 3TF and comprising inductance PL and resistance PR applies frequency to the input of Thyratron tube TR. by means of transformer 5TF A phase shifter comprising inductance PL and resistance PR connects the secondary winding of transformer 3TF to the input circuit of Thyratron tube TR by means of transformer 5TF so that frequency is applied to the input of tube TR Other components may be used, such as resistdrop over the resistance PR is a lagging voltage, lagging less than .90 degrees behind the impressed voltage. This voltage itself, (not the voltage drop, the current in this resistance PR flowing against the voltage across this resistance) with respect to the voltage in the secondary winding of this transformer (swinging the vector through an angle of 180 degrees) is however a leading voltage, leading more than degrees the impressed voltage. If this leading voltage is then combined with the voltage in the upper portion of the secondary winding the resultant vector sum is a leading voltage, leading probably less than 90 degrees and to an extent to properly fire the tube. V s v Indication lamps G, Y and R, assumed to be green, yellow and red respectively, are shown connected to the contacts of relays F and F and it will be understood that the circuits controlled by these two relays may be used forother purposes such as the automatic control of brake valves or the like.

Operation of Fig. 1

The lines indicatedv green, green, yellow and red appearing above and parallel with the track, indicate the signal which will be displayed by the car-carried apparatus when corresponding sections of track are traversed and avehicle W is occupying section D.

It will first be assumed that track section D is occupied as illustrated by the presence of wheels W assumed to be associated with a train in this section. The shunt across the rails of this section provided vby such a train deenergizes track relay T which energizes the primary winding of transformer IT with alternating current of frequency f over a circuit extending from one side of the current supply of frequency f back contact 20 of relay T and primary winding of transformer TT to COM, which is assumed to be the common terminal of supply currents of frequencies f and f as clearly indicated in Fig. 2.

Track relay T associated with block C remains energized due to the flow of direct current from battery B and frequency f is applied to section B by way of transformer 'IT and resistor R Transformer TT is energized with frequency f over a circuit extending from one side of this frequency circuit, front contact In of relay T and primary winding of transformer TT to COM.

Track relay T remains energized because of direct current in track section B from battery B and frequency f is connected to the primary winding of transformer TT by Way of front contact [5 of relay T. Frequency f is applied to section A from the secondary winding of transformer TI and the limiting resistance R in series with battery B. It will be understood that frequency i applied to the rails of section C and frequency I applied to the rails of sections B and A have no effect on the direct current track relays.

With the vehicle having receiving coils RC and RC in section A as illustrated, frequency f flowing in series through the rails of this section induces currents of frequency f in the-windings of these two receiver coils, from where it is impressed on the primary windings of transformers IITF and IT)? becausebandpassfilters BPF V and BPF allow either of the'frequencies f and f to pass. Y

' The voltage of frequency f induced in receiv ing coil RC is amplified by voltage amplifier ll'iA because this frequencyis impressed on its input circuit by way of the secondary winding of transformer ITF this circuit being tuned to frequency f by condenser 10 Frequency i ls; applied to the input circuit of power amplifier PA by means oftransformer 2TF the input'circuit of this power amplifier being tuned to frequency f by condenser 3C 4 Frequency f amplified by tubes WM and PA is applied .to the plate circuit of tube 'I'R having relay F in series therewith, by means of transformer 4TF and because of the voltage and power amplification of this frequency, a voltageof considerable magnitude of frequency f is applied to the plate of tube TR. 1'

. Frequency fl is induced in receiving coil RC and is amplified by voltage amplifier ZVAP-and from the output circuit of this tube the amplified .voltage is applied to theinput of tube TR by means of transformer 3T1 l2, the upper phase shifter PR, PL and transformer 5TF H I Since the Thyratron tubes are of the positive control type and since the plate and grid 1 circuits are both controlled from the same source, the proper phase relations must exist between the voltages applied to these circuits to cause the tube to rectify andpassplate current. Ob-

viously if the grid voltage is displaced (leading or lagging) exactly 180 degrees with respectto the plate voltage no firing can take place, because no positive grid control voltage is present through any part of the positive swingof the plate voltage. Since it, would be desirabletofire the tube at theearly part of a positive swing of the plate voltage the grid voltage is preferably of a phase to lead the plate voltage, to an extent so' that it is of an appreciable-positive value when the plate voltage enters upon a positive swing. During eachpositive voltage swing of the upper terminal of the secondary winding of transformer 4TF with respect to its lower terminal, positive potential is applied to the plate of tube TR isapplied to the grid circuit of tube TR and the phase of this voltage with respect to that ap The proper magnitude of voltage "5 plied to the plate is so determined by the'upper phase shifter PR -LR to cause this grid voltage to lead between say 10 and 90 degrees the voltage applied to the plate, as above pointed out, whereby the tube is fired and plate current flows for operating relay F The relation between the direction of turns in the primary andsecondary windings of 'transformers lTF 2TF 3TF 4TF 5TB, ITF 2-'IF 3TF 4TB and 5TB is preferably such that if current of frequency f is flowing in the track'circuit the grids of tubes lVA PA and 2VA will have'the voltage applied theretoswing positive at *sub- I stantially'the same time as will also the alternating voltageapplied to the plate of tube -.TR but the voltage applied to the grid of tube TR will, by reason of the inclusion of the phase shifter PR PU, have this voltage applied'thereto swing positive earlier to an extent of say from 10 to 90 degrees. I The same relationship is true of tubes lvA PA ZVA and TR when frequency f is applied to flow in the track circuit.

During each negative swing of the voltage on of relay F and lamp G, to

augmented by the tuning of relay F by condenser 4C A a 1 Since frequency f is not being received, relay F2 is. not energized. A circuit is closed for lamp G which extends from front contact ll When the train movesinto section B, quency f continues to be received because front contact ID of'relayT is closed and relay F remains picked up for lighting lamp G.

When the train moves into section C, the received frequency is changed to I because back contact 20 of relay T is closed. Frequency f is amplified by voltageamplifier IVA and power amplifier PA and then applied to the plate circuit of tube TR to which relay F isconnected.

Frequency f is also amplified. by voltage amplifier 2VA and applied to the input of TR by way of the lower phase shifter PR PL all in a similar manner already explained for tube TR Relay F is energized by positive swings of the plate and it remains picked up .during negative swings of the plate. In this case frequency f is not received, relay F remains down and a circuit is closed for lamp Y, extending from back contact ll of relay F front contact l2 of relay F and lamp Y, to

When the train moves into occupied section D, neither frequency I nor f is received because of the short circuit ahead of coils RC and RC provided by W In this case, relays F and F both drop and lamp R is lighted over a circuit extending from back contact H of relay F back contact l2 of relay F and lamp R, to

From the above description it will be observed that the grid voltage must be in proper phase relation with the plate voltage and of sufficient magnitude to overcome the bias provided by the circuit including the associated rectifier R'IE'for the Thyratron tube to fire and the associated relay to operate. Considering frequency for example, failure of either the proper phase relation or the failure of any one or more of the tubes IVA PA 2VA and TR will cause relay F to release and light lamp R, which is a danger indication.

Considering frequency f failure of either the proper phase relation or the failure of any one or more of the tubes IVA PA 2VA and TR will prevent theoperation of. relay F so that yellow lamp Y cannot be energized and lamp R will be lighted because frequency f is not being received. It will thus be seen that it requires the reception of the authorized frequency to give the proper signal indication and that the loss of either frequency, when it should be received, gives the red or danger indication.

In the event of a broken rail in the block ahead of a train, the loop circuit including the track rails is open and no current is received for picking up either F or F consequentlythe red lamp is energized. I U

Stray currents ordinarily exist inonerail and ground or in both rails and ground, so that they do not fiow over the loop circuit for causing response of the receiving apparatus and the resultant operation of an F relay. In other words, ,the proper frequency must flow up one rail and fredown the other to operate a signal control relay and this'is due.;t0 the-fact that instantaneous voltages of the proper frequency must appear across the terminals of both coils RC and RC? in proper. phase to cause the pick up operation of a relay. Modification 'The above description relates to a three indication arrangement, that is, the lighting of lamp G, lamp Y or lamp R in response to the receipt of frequency f f 'or neither, respectively. It will now'be explained how a fourth indication is provided, which indication requires the receipt ofboth frequencies f and f The modification illustrated in Fig. 4 has certain portions of the apparatus and circuits illustrated in block diagrams because the apparatus andcircuits represented by these block diagrams are the same as illustrated in detail in Fig. 1.

In Fig. 4, for example, the block labeled BPF refers to the same band pass filter illustrated means of dotted lines associating them with the respective blocks.

The trackway apparatus and circuits are modified to provide the fourth indication and in the following explanation the conditions assumed in connection with Fig. 1 will be considered in connection with Fig. 4, but in reverse order. It will first be explained how the red lamp is lighted when the train carrying receiver coils RC and ,RC enters block D, with this block occupied as indicated by wheels W With blocks A, B and C unoccupied and block D occupied, track relay T is deenergized and relays T and T are energized. The circuit to relay D is interrupted atopen front contact 50 so that relay D has its neutral contacts in their dropped away positions. Relay D is energized in the proper direction for picking up its neutral contacts and for positioning its polar contacts to the left as shown, over a circuit extending from (CN), winding of relay D front contact 5| of relay T and-back contact 52 of relayT to (B). Relay D is energized in the proper direction for picking up its neutral contacts and for positioning its polar contacts to the right over a circuit extending from (3+) front contact 53 of relay T front contact 54 of relayT and winding of relay D, to (CN) As indicated bythe notations immediately above the track, a train entering block D will receive the red signal indication because no current is received on the car carried apparatus and relays F and F are deenergized, which closes a circuit for lighting lamp R extending from back contact ll of relay F back contact l2 of relay F and lamp R, to

A train entering block C will receive the yellow indication, this being due to the receipt of frequency f by the car carried apparatus. Frequencyj is applied to section C overa circuit which may be traced from the right hand -upper winding of transformer 9TF through battery 33 to the lower rail and from the left hand terminal of the upper winding of transformer 9W,

through resistance R to the upper :rail. Thesecondary of transformer 9TF has frequency J induced therein because of the energization f its primary winding over a circuit extending from one side of the source of frequency f lower wind- ,ingof transformer 9TF and backcontact 55 of relay .-D to the other .side of the source indicated COM. At this time the secondary winding of transformer 9T1 is short-circuited at back contact 56 of relay D for the purpose of removing the impedance of this winding from the track circuit, in order that the circuit constants of the track circuit may be of proper value for the most efficient transmission of frequency f It will be observed that frequency f is not applied to the primary winding of transformer S'IF because 'of open front contact 55 of relay D The circuits associated with the exit ends of blocks A, B, and C are the same and it will :now be pointed out how frequency f is applied to section B. The primary winding of transformer 8T1 is energized from the ,7 source of current over an obvious circuit including front contact '65 of relay D former llTF is not energized with frequency j because of open back contact 65 andbecause'contact -61 of relay D is in its left hand position. The secondary winding of transformer 8TF is short-circuited to remove its impedance, by means of acircuit including frontcontact 56 and contact 58 of relay D in its left hand position. Frequency f is applied to the lower track rail of section B over a circuit which may be traced from the right hand upper terminal of transformer 8'I'F front contact '66 of relay B contact .68 of relay D in its left hand position and battery B The other side of this frequency source is :con nected to the upper track rail over a circuit extending from the left hand upper terminal of transformer 8T1 and resistance R Both frequencies f and f are applied to the rails of section A under the condition assumed, both zsecondary windings on transformers :l'IF and I'I'F having the short-circuit removed therefrom because of contacts 16 and "1,8 of .relay i-D being in the positions illustrated. The primary winding of transformer ITF is energized from one side :of the source of frequency f lower-winding of transformer I'I'F contact .H of relay D in its right hand position and front contact 9 of relay D, to the other side of the source of .frequency f indicated-COM.

The lower winding of transformer 'I'I'F is'energized from the source of frequency f overan obvious circuit completed at front contact of relay D. Since neither secondary winding of transformers lTF nor TIE- is short-circu'ited, they are connected in series and to the track rails of block A by means of an obvious circuit.

It has already been pointed :out that the :red or most restrictive indication is provided by ilighting lamp B when neither frequency I nor f is received, thus effecting the dropping of both 'relays F and F The next most restrictive indication (yellow) is given when frequency ;;f is transmitted to the car carried apparatus, ;in which case this frequency is passed through band filters BPF and BPF by way of transformers and condensers lTF 2C and -I-F --l C to voltage amplifiers 2-VA and-IVA respectively; Theamplified frequency is transmitted from the outputs The primary winding of trans.-

,of'these two voltage amplifierszby way of "transformer 3FI F =to;phaseshifter zandby way-of transformer condenser combinations 2'I -F '3C and gpower amplifier PA to transformer 4'I F The output of phase shifter? passes frequency scribed operation relating to the transmission offrequcncy f to the car carried apparatus is the same as in the arrangement of :Fig. 1. Relay T is therefore picked up and relay F is dropped away (because frequencyj is not being ireceived') and lamp Y :is lighted oven-a circuit extending :from (-1-), front contact ll of relay :F back contact 13 of relay F and :lamp Y, to (-1.,

A train in section B receives frequency J2, which is transmitted :by an arrangement similar to that described in connection withyfrequency F, for applying proper energy to the output of tube 'and energy :of-the :proper phase to the input of tube TR. for picking up :relay F .Since frequency if is :not :being received, relay- F is down and relay {F is picked :up for 'closingia :cir-

cuit through back contact :H :and :front'contact ll-2 for lighting rlamp =In the Fig. 4 arrangement, transformer 4W has an additional secondary winding leading through the directional filter tothe primary winding of transformer -6'IFl. ifimce the secondary of transformer {6W1 is connected to the input-circuit of tube, f-IR i, frequency J is applied to the input circuit 'of this tube. Furthermore, transformer Ill-TF has an -.additional secondary winding which leads to the primary-wind- -ing of transformer :B'I F'Z. One secondary wind, ing :Lof transformer S'IF supplies plate :energy to tube 'I'R with relay F connected i-n ith'e plate circuit. Another secondary windingof transformer is :connected in series with the secondary winding of transformer GT-F and the input circuit of tube TR. r

The above arrangement of :the circuits ,-for tube EUR- provides a means for picking up relay F by combining plate energy developed at frequency f with :gridfiring voltage developed H at frequency f 'The *grid voltage for tube 'TR i :derived by combining frequency provided by transformer GTF 180" out of phase with frequency f :(the same frequency) applied to the plate circuit of tube TR, with :a "voltage of frequency 7 'developed. by power amplifier PA' and supplied :to the input circuit of tube IR from the extra winding of transformer '4TF 'b-y way of the directional filter. With-this-arrangement, :the component of grid voltage idueato' fro-'- :quencyrf makes tube TR inoperable during intervals when f is receivedalone; is because, "as above mentioned, the grid and plate voltages supplied to TR from transformer are 180 out of phase. Combining this ag'l'id voltage with the voltage produced by J -(through the directional filter) causeswth'e firing of the tube and the picking up of relay F The directional lfilterj-is for the purpose of preventing feed back from the circuits containing frequency 1 to the circuits :containing ifrequency. f and it will be understood that a one way repeater, repeating fromleft to right, could be used in place of the directional filter.

Sincefrequency f is received, relay F is picked up, since frequency f is received, relay F is picked up and as above described,relay F is picked up because of the receipt of both frequencies f and P. The circuit is now closed for lighting lamp G whichextends from front contact ll of relay F front contact l3 of relay F front contact I 4 of relay F and lamp G, to

From the above description it will be observed that a double check is provided for the'green signal indication, that is, relays F F and F must all be picked up to light this particular lamp. The systemvvould operate without relay F by connectinglamp G to front contact [3 of relay F which would require both relays F and IE picked up and the receipt of both frequencies f and f to light the green lamp. However, in the present arrangement one 'or the other of relays E and F could stick in its operated position, with the other one receiving an authorized frequency, without operating the cleared signal, because relay F would be down and thecircuit to lamp G opened at front contact l4. g V

It is obvious that the invention may be embodied in a variety of other forms without departing from the spirit or essential attributes thereof and therefore I do not desire to'be limited to the exact modification shown and described but contemplate all variations thereof that come within the "scope of the appended claims. I i i What I claim isi- 3 1. A system of continuous inductive control for railway vehicles comprising; in combination with a track circuit including two track rails provided with alternating current of one'of a plurality of different frequenciesappliedacross the rails at the exit end of a section of track and flowing in opposite directions in the rails; two receiving coils on the vehicle each inductively associated with a different track rail, vacuum tube detecting and amplifying means on the vehicle for detecting the magnitude and the phase relation of the potentials induced in said receiving coils, and means distinctively responsive to currents delivered by said detecting and amplifying means depending on the particular frequency of said plurality of frequencies flowing in the track rails and the phase relation of the potentials induced in said receiving coils at a particular time.

2. In combination, a railway track,"a source of alternating current connected across the two track rails at the exit 'end thereof, two car carried windings one in inductive relation with one and the other in inductive relation with the other of. said two track rails respectively, and train governing mechanism including a phase controlled gaseousar'c discharge device having its plate circuit energized in response to current induced in one of said windings and having its grid activated in accordance with current induced in the other of said windings and responsive only to the energization of both windings in response to current flowing through the two track rails in opposite directions.

3.In combination; a car carried receiving apparatus including two receivers for receiving indications in accordance with track conditions; a source of alternating current energy applied across the rails of the track at the exit end of a section so that current flows in oppositedirection's in the track rails, said apparatus including an electrostatically controlled arc discharge device having its in-put and out-put circuits energized byamplified energy derived respectively from the two receivers one in inductive relation to one track'rail and the other in inductive relation to the other track rail; and means for determining the phase relation of the energy applied to said in -put and said out-put circuits so that said device is rendered active only when the alternating currents in the track rails flow in opposite direc tions.

4. In a train control system for railroads; trackway apparatus for selectively applying alternating currents of one or more of different frequencies to the rails in series so as to flow in opposite directions in the track rails and of a frequency or frequencies in accordance with trafiic conditions; two car carried receiving coils one over one rail and the other over'the other rail for receiving currents of said frequency or frequencies from the rails; de-coding means on the car controlled by said receiving apparatus and selectively responsive to said different frequencies for; delivering currents characterizing varying restrictive traffic" conditions, said de-coding means including a plurality of phase controlled vacuum tubes selectively responsive to currents induced in said coils of said different frequency or frequencies only if these currents are in response to currents flowing in opposite directions in said rails; and signals controlled by said de-coding means for causing the display of the most restrictive indication in the absence of currents of any of said frequencies.

' 5. In a train control system'for railroads; trackway apparatus for selectively applying to the rails at the exit end of a section an alternating current of a first frequency; a second frequency or both frequencies concomitantly as determined by traflic conditions so as to cause such current to flow in opposite directions in the track rails; car carried receiving apparatus for receiving currents of said frequencies from the rails including two receiving coils one inductively associated with one track rail and the other inductively associated with the other track rail; de-coding means on the car controlled by current from said receiving apparatus and selectively responsive to current of said first flowing in opposite directions in said track rails;

and signals controlled by said de-coding means to display the least restrictive indication when said currents of plurality of frequencies are simultaneously received.

6. In a train control system for railroads; A

trackway apparatus for selectively applying across the rails at the exit end-of a track section an alternating current of a first frequency,a second frequency or both frequencies concomitantly as determined by traffic conditions; car carried receiving apparatus including a coil over each rail for receiving currents of said frequencies from the rails; de-coding means on the car controlled by said receiving apparatus and selectively responsive to current of said first frequency, said second frequency and both of said frequencies concomitantly, said de-coding means including electrostatically controlled detectors and amplifiers which'have their electrode circuits individually connected to said coils and are selectively responsive *to currents induced :in' said coils of :said frequencies singly and combined only :when flowing in opposite directions in said rails; and signals controlled by said de-coding 'meansfor in'the absence of currents of both of said frequencies causing the display a most restrictive indication.

7. In a train control system for railroads; trackway apparatus for selectively applyingto the rails at the exit end-ofasectionof track alternating current of either or both :of two ,difierent frequencies as determined bytraffic conditions; car carried apparatus including two receivers one in inductive relation with one track rail and the other in inductive relation with the other track rail energized by saidalternating-currents in said rails; two electronic tubes each having a plate element and a grid element and each having one of its elements activated in response to voltage induced in one of said receivers and having its other elements activated in accordance with voltage induced in the other of said receivers; a first relay and a second relay each controlled by one'o'f -sa'id tubes and each responsive if current of a different one of said frequencies flows in said rails; and means controlled by said relays for distinctively displaying danger, caution and clear indications in accordance with whether current of neither frequency, current of one frequency or current of both of said frequencies, respectively, is flowing in the rails of said section.

8. In a train control system for railroads; a plurality of blocks; means associated with each block for selectively impressing across the rails at the exit end alternating current voltages of one of several frequencies determined by the condition of traffic in the next block in advance to cause current to flow in opposite directions in the track rails; a pair of car carried receiving coils disposed in front of the first pair of wheels and axles of the car one in inductive relation with one rail and the other in inductive relation with the other rail; a pair of gaseous arc discharge tubes each having a grid circuit and a plate circuit and each having one of its circuits controlled by one of said coils and having its other circuit controlled by the other of said coils; indication receiving means controlled by said tubes; means including circuit connections between each of said coils and both of said tubes for applying voltages of a pre determined phase relationship to the grid circuits and the plate circuits of said tubes so that currents of a definite phase relation must exist in said coils as obtained only if currents flow in opposite directions in said track rails to energize said indication receiving means.

9. In a system of cab signals or train control for railroads, in combination with a railway track having its rails divided into blocks; means for causing the flow of alternating current in opposite directions in the rails of each block; car-carried apparatus including one receiver over one of said rails and another receiver over another of said rails; an electronic tube on the vehicle having its plate circuit energized externally of the tube in accordance with voltage induced in one of said receivers and having its grid circuit activated in accordance with the voltage induced in the other of said receivers; and indicating means controlled by the out-put circuit of said tube.

10. In a system of cab signals or train control for railroads, in combination with a railway track divided into blocks; a track circuit for each block including a source of direct current connected across the rails at the exit end and-a direct current relay connected across the rails at the encurrent in opposite directions in said rails; car'- carried apparatus including a receiver over zone rail and another receiver over the other rai l; an electronic tube on the vehicle 'hav ing its plate circuit energized externally of the tube "in accordance with voltage induced in one of said receivers and having its g-r-id circuit activated in accordance with "the voltage induced the other of said receivers; and indicating means controlled {by the out-put circuit of said tube.

ll. Ina system of cab signals or train control for railroads, in combination with a railway track divided into blocks; means for causing the flow of alternating currents of two different frequencies in opposite directions in the track ra'iis;

car-carried apparatus including a receiver over one rail and a second receiver over the other rail; an electronic tube on the vehicle having its plate circuit energized in accordance with alternating voltage of one frequency induced in one of said receivers and having its grid circuit activated in accordance with alternating voltage of another frequency induced in the other of said receivers; and indicating means controlled by the out-put circuit of said tube.

12. In .a system for controlling cab signals or brake control apparatus on a railway vehicle; in combination with a pair of track rails comprising the rails of a track circuit energized from the exit end to produce the flow of alternating current in opposite directions in said track rails; means for applying current of one frequency or current of another frequency to such track circuit depending upon traffic conditions in advance; car-carried apparatus including two receivers one located in inductive relation with one of said track rails and the other located in inductive relation with the other of said track rails; an amplifying means for each receiver for amplifying the voltages induced in said receivers; and two electronic tubes, one of said tubes having its plate circuit potential derived from one of said amplifying means and having its grid circuit activated by potential derived from the other one of said with whether one of said electro-responsive means, the other of said electro-responsive means, or both of said electro-responsive means are energized.

13. In a system for controlling cab signals or brake control apparatus on a railway vehicle; in combination with a pair of track rails comprising the rails of a track circuit energized from the exit end to produce the flow of alternating current in opposite directions inthe rails; means for applying current of one frequency or the other frequency to such track circuit depending upon trafiic conditions in advance; car-carried apparatus including two receivers one located in inductive relation with one and the other located in inductive relation with the other of said track rails; an amplifying means for each receiver for amplifying the voltages induced in said receivers; and two electronic tubes, one of said tubes having its plate circuit potential derived from one of said amplifying means and having its grid circuit activated by potential derivedfrom the other one of said amplifying means, and the other tube having its plate circuit potential supplied from said other of said amplifying means and having its grid circuit activated by said one of said amplifying means; an electro-responsive means included in the out-put circuit of each of said tubes;

and car-carried apparatus controlled in accordance with whether one of said electro-responsive means, the other of said electro-responsive means, or neither of said electro-responsive means are energized, respectively.

14. In a system for controlling cab signals or brake control apparatus on a railway vehicle; in combination with a pair of track rails comprising the rails of a track circuit energized from the exit end to produce the flow of alternating current of either or both of two frequencies in opposite directions in the track rails in accordance with traflic conditions in advance; car-carried apparatus including two receiving coils one located in inductive relation with one: track rail and the other located in inductive relation with the other of said track rails; an amplifying means for each receiving coil for amplifying the voltages induced in such coil; three electronic tubes on the car, one of said tubes having its plate circuit energized by alternating potential of one frequency derived from oneofsaid amplifying means and having its grid circuit activated by alternating potential of said one frequency derived from the other one of said'amplifying means, the second tube having its plate circuit energized by alternating potential of the other frequency supplied from said other of said amplifying means and having its grid circuit activated by alternating controlled by the out-put circuits of said electronic tubes.

WALTER H. I-IOPPE. 

